Dongguan Hengqing Electronics Co., Ltd. , http://www.chbluetooth.com
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Analysis: Dangerous areas of electronic ballasts
Have you ever encountered this situation? You have completed the design of a large-scale lighting renovation project that uses advanced electronic ballasts to replace the old magnetic ballasts in thousands of fluorescent lamps. Customers are looking forward to saving energy, reducing maintenance costs and achieving better lighting results through this transformation. However, electrical contractors have discovered significant problems in your design because the components of the lighting control system have begun to become damaged during installation. In response to this problem, people quickly found that the mechanical relay contacts were fused together, but why did this happen? The circuit is designed in accordance with the requirements of the National Electrical Code (NEC). The contractor is constructed in strict accordance with the engineer's drawings. The electronic ballast is included in the UL-listed product, and the rated load of the lighting control relay. The selection design is reasonable. Why do the contacts of the relay melt together? This is caused by the inrush current of the electronic ballast. 2. Knowing the surge current The surge current is not a new problem for the lighting designer. In the IES lighting manual, it can be easily found that the tungsten filament of the incandescent lamp has a relatively low resistance in the cooling state, when the first electric energy is supplied. At the time, the amount of current passing through the tungsten wire is 20 to 25 times larger than the amount of current passing through when the tungsten wire reaches the normal operating temperature. Fortunately, this usually happens within a few milliseconds. Mechanical relays designed for incandescent lamp loads therefore typically have oversized contacts to accommodate the initial impact of this current. Surge current has little effect on the core and coil ballasts used in fluorescent lamps. The current flowing into the lamp is controlled by an inductor that has a higher impedance when power is first supplied. The amount of inrush current can usually be limited to 10 times or the operating current value in less than 10 ms. Therefore, circuits designed for incandescent lamp loads are also suitable for handling surge currents caused by ordinary ballast loads of fluorescent lamps. With the development of technology, the National Appliance Energy Protection Regulations have almost eliminated conventional magnetic ballasts. The latest design is electronic ballasts. The electronic ballast has the advantages of compact size, low energy consumption, elimination of stroboscopic light, and dimming characteristics for advanced lamps. The reliability of electronic ballasts has been addressed in earlier designs, and the only remaining legacy is the inrush current problem. 3, simple electronic ballast design concept Electronic ballast design concept is relatively simple. But there are still two major issues that need to be addressed. The first problem is that current can flow into the capacitor only when the input voltage from the ballast is greater than the voltage of the capacitor. At the peak of each AC cycle, the capacitor is fully charged, resulting in an input current that is not a sine wave, causing a large amount of harmonic distortion in the converter. This can cause the power line to overheat, causing great trouble to the utility company. Ballast manufacturers have two design options when dealing with this issue. The first design choice is to install a passive filter consisting of an inductor, a capacitor, and a resistor, placed in front of the A/D converter in the circuit. This filter allows current to flow smoothly into the bridge full-wave ballast to produce a sine wave that controls the total harmonic distortion (THD) between 20% and 30% (this also helps to improve the ballast Power factor). The second design choice is to use an active filter that is mounted after the bridge full-wave rectifier. This is actually an electronic switch that both filters the current flowing into the capacitor and provides a high power factor for the electronic ballast. Manufacturers of ballasts are often willing to choose active filters for several reasons: active filters can control harmonic distortion to be lower than passive filters, typically less than 10%. More importantly, the active filter using electronic components has the advantages of being cheaper than passive filters, being filial and light, and saving energy.